1. Field of the Invention
The invention is directed to the field of subsurface drilling with the use of high pressure fluid for the installation below ground of various utility items such as electrical cable, conduit, water pipes, sewer pipes and the like.
2. Description of the Prior Art
When the land has no structures, plantings, parking lots, etc., upon it, the usual quickest and least expensive method for underground installation of utility items such as electrical cables, conduit, water pipes, sewer pipes and the like is to cut or dig a straight sidewall trench of the appropriate depth, lay the object at the trench bottom and cover it with the soil removed during the trench formation. The trench is quickly dug using mechanized equipment such as trenchers, front loaders, bulldozers or the like, or dug manually.
However, when the land has been improved, installation, removal and/or replacement of below-ground utility items to avoid damage or destruction to any such improvements is both slow and expensive. Often, space and access limitations prevent any methods other than manual trenching from being used. In addition to the work itself, there is the disruption of land use and the expense of restoring the trenched area to its former appearance.
In an effort to minimize surface disruption and minimize the costs of surface reconstruction, devices have been developed to bore beneath the surface of land and create a bore hole into which cable, conduit, pipe or the like could be inserted without disturbing the surface of the land or those structures thereon. A first type of device was created to permit the replacement of electrical cables and used those cables to guide their movement through the soil which was removed by means of one or more fluid jets. The old cable was pulled from the bore and a new one inserted. A tool of this type is shown in U.S. Pat. No. 4,385,667 issued May 31, 1983 and in U.S. Pat. No. 4,403,667 issued Sept. 13, 1983.
Although this type of device works well for previously installed electrical cable replacement, it is not suitable for new cable installations because there is no cable to follow and thus no means to independently guide the tool.
U.S. Pat. No. 4,306,627 issued Dec. 22, 1981, shows and describes a tool which can be used for a new installation. A rotating fluid jet drilling nozzle is advanced by a pipe string in much the same manner as a rock drill is employed to dig oil or gas wells. Despite mechanisms to control the position of the nozzle, as is shown in U.S. Pat. No. 4,674,579, issued June 23, 1987, it is still difficult to steer the boring head mounted at the end of a pipe string required to push and advance the boring head. Specifically, the angle that the nozzle and head is placed in, in relation to the longitudinal axis of the pipe string, is fixed. Such a fixed angle adds difficulty in varying the radius of the turn.
A particular disadvantage of the system described in the '579 patent is that if too sharp a radius is attempted to be made, the next successive section of pipe may bind as it advances to the area where the head formed the tightest radius. This then requires additional more complicated cutting steps in order to navigate turns in such areas.
The present invention, rather than being dependent solely upon fluid cutting for steering, as provided in the '579 patent, instead utilizes fluid pressure to effect a positive action on the drill head to thereby direct the drilling head in the desired direction. By causing the drill string pipe itself to effect this movement over a longer radius, it lessens the likelihood of subsequent pipe strings binding at the turning point.
In applicant's copending application Ser. No. 07/115,987, filed Nov. 2, 1987, now U.S. Pat No. 4,905,773, there is disclosed both method and apparatus of controlling the direction of a subsoil boring tool. In such application, a series of four circumferentially arranged hydraulic pistons are used to both cooperatively push and pull and thereby turn the boring head in the desired direction. Though this device works well, it requires separate hydraulic and electric lines along with solenoid valves to provide adequate control. Such a boring tool, having numerous hydraulic and electric devices and lines, are expensive to manufacture and complicated to operate, and may not conveniently be used with the "pipe string" type drilling where new sections, without attendant control lines, are constantly added as the boring head advances.